Whole-house surge protectors

This whole-house surge suppressor is mounted beneath the circuit breaker panel in Jim Dulley’s house. This 20-ampere circuit breaker has surge suppression built into it. Photo credit: James Dulley

People often think of only electronic gadgets, such as computers, game consoles and audiovisual items, as being at risk from electrical surges. Actually, nearly every electric item in a house today has sensitive electronics that can be damaged by a surge. These include kitchen ranges, dishwashers, vacuum cleaners, air conditioners and fans.

A common source of an electrical surge is lightning. The voltage and current spikes from just a single lightning strike are enormous, and there are typically many during a thunderstorm. If your house and wiring experience a direct or very nearby lightning hit, even a good surge suppressor will probably not be able to protect all electronic items.

When a storm is forecast and you begin to hear thunder, unplug as many of your electronic devices as possible. Just switching them off may not be adequate protection from voltage and current surges. A huge voltage surge can arc across an open switch and still fry the electronic components in an expensive device.

Many times, it's the repeated smaller electrical surges that damage electronic equipment. These can be generated by the switching on and off of inductive equipment (usually electric motors) in nearby businesses. Some of these smaller surges can even be generated by motors from your own vacuum cleaner, refrigerator compressor or clothes washer through your home's wiring.

It usually takes a long time for these numerous smaller surges to cause failures. The wire and circuit board insulation can slowly break down from each small surge and normal aging. Eventually, a wire may short out or the electronic component begins to malfunction and the device fails. These surges can also reduce the life of many types of light bulbs.

Whole house protection

There are several types of whole-house surge suppressors designed to protect all of the wiring circuits in a house. Some mount on the circuit breaker panel indoors or are built into a circuit breaker. Others are designed to mount at the base of the electric meter. I recommend hiring an electrician to do the installtion.

There are differences in their protection. A common design uses metal oxide varistors (MOV) to dissipate the surge before it flows through the house wiring. Think of it as a floodgate. At normal voltages, the gate is closed, preventing leaks. But if the voltage gets too high, the gate opens, allowing the excess damaging current to pass to ground, protecting the equipment.

If the components (including MOVs) in a surge suppressor are too small, they can't handle the surge, and they fail. Using larger components, rated to handle more Joules (a measure of energy), allows the suppressor to safely dissipate a larger surge. When comparing surge suppressors, a higher number is better for the total energy dissipation. Clamping voltage is the voltage that is required for the "floodgate" to open — for the MOV to conduct electricity. A lower number for this is usually better.

Even though the surge suppressor can protect your electronics, a large surge may burn out the MOVs. Many models have a light to indicate if they are still functioning. Check it, especially after a thunderstorm.

The following companies offer efficient surge suppressors:

It's important to note that electronic devices like computers and entertainment systems have multiple connections, including satellite or cable, phone or network, in addition to the power connection. Any can serve as a path for a surge to cause damage. Surge suppression installed on the power line doesn't guarantee protection.

For the most sensitive electronic devices, also use point-of-use surge suppressors for extra protection. They are inexpensive and let you completely switch off the power to save electricity when the device is not being used. Look for models tested for compliance with Underwriters Laboratories (UL) Standard 1449, or ask your local electric cooperative for advice.

About the Author

James Dulley is an engineer and syndicated columnist for the National Rural Electric Cooperative Association. www.dulley.com

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